Detecting the presence of pathogenic microbial species requires, as a first step, collection of an appropriate sample. Typically a sterile collection device such as a swab is used. In the past, these swabs have been made of various materials such as cotton, sheep wool, polyester and rayon.
After the sample has been collected on a swab it is transported to a microbiology laboratory where any organisms present are identified. The identification method may be conventional culturing followed by identification or immunometric assay. A persistent problem for samples to be cultured has been maintaining viability of pathogenic organisms. Where the sample is to be processed for an immunoassay, a persistent problem has been recovery of immunologicaly active material. Additionally, the sample needs to be protected from contamination by the environment during transport. Numerous devices have been devised that provide both a means for obtaining the sample and means for protecting the sample during transport. Most often these devices comprise a swabbing element having a shaft typically of wood or plastic and a swabbing tip which has universally been produced from fibrous material such as cotton fibers, wool, polyester fibers or rayon fibers.
Further elements common to most devices are a cap to which the shaft is fixed and which mates with a lower swab cover to protect the swabbing tip both before and after collection of sample and a liquid medium containing reservoir such as a frangible glass ampoule that can be broken to release aqueous medium to keep the swab and sample moist. Representative collection and transport devices are shown in U.S. Pat. Nos. 4,223,093 (to Newman et al.), 4,030,978 (to Abramson), 4,175,008 (to White), 4,311,792 (to Avery), and 4,014,748 (to Spinner et al.).
Media described by Stuart et al. "The Problem of Transport of Specimens for Culture of Gonococci," Can. J. Pub. Health, vol. 45, pp. 73-83 (1954) and a later modification by Amies "A Modified Formula for the Preparation of Stuart's Transport Medium", Can. J. Pub. Health, vol. 58, pp. 296-300 (1967) are examples of growth maintenance media which do not promote growth that are commonly employed. Such media preserve the organisms present in the specimen while retarding or preventing growth during transport.
The medium is often retained inside the specimen collection device and adjacent to the specimen collection swabbing tip by an absorbent fibrous swatch of material. This swatch or pledget, as it is often named, can be a woven or non woven section of fabric or a piece of fibrous material such as cotton or rayon. While serving to restrain the flow of the aqueous media and prevent dehydration of the collected sample, the pledget materials such as cotton, polyester or rayon currently utilized do not enhance and may possibly be detrimental to preserving the viability of the microorganisms collected.
Several studies have attempted to evaluate the toxic nature of various fibrous materials used in the swab and also employed in the pledget. Studies are reported by Ellner et al. "Survival of Bacteria On Swabs", J. Bacteriol., vol. 91, pp. 905-6 (1966); Barry et al. "Efficiency of a Transport Medium for the Recovery of Aerobic and Anaerobic Bacteria from Applicator Swabs," Appl. Micro. Bio., vol. 24, pp. 31-3 (1972); Ross et al. "Swabs and Swab-Transport Media Kits in the Isolation of Upper Respiratory Bacteria," J. Clin. Pathol. vol. 35, pp. 223-7 (1982); Rubbo et al. "Some Observations on Survival of Pathogenic Bacteria on Cotton-Wool Swabs," Brit. Med. J., pp. 983-7 (May 1951), and Anderson "Antibacterial Bacteriological Swabs", Brit. Med. J., pp. 1123-4 (Nov. 1965).
Certain devices have eliminated the need for a liquid retaining pledget by substituting an agar containing medium for the liquid medium. The agar produces a gelled or highly viscous medium into which the specimen swab is placed after collecting the sample. The agar medium provides protection, but leads to agar residue on the swab. This residue can subsequently interfere with analytical procedures such as specimen staining for visual microscopic detection of organisms. Agar has also been found to interfere with certain latex agglutination tests commonly employed. Stuart et al. (cited above) have shown agar to be toxic to certain organisms.
A very recent study, Appelbaum, Peter C. et al., "Survival of Bacteria in Difco CultureSwab and Marion Culturette II Transport Systems," J. Clin. Micro. Biol., vol. 26, pp. 136-8 (1988), typifies the commercial "state of the art" in describing two commonly available commercial systems with fibrous swabs and a media component. This study points out that 90% of the organisms cannot be recovered from either wet system after four hours storage time.
Devices having a liquid transport medium are expensive to make because they have multiple elements which must be formulated or made and then assembled. The devices with agar transport medium are less than acceptable because the agar interferes with subsequent testing. Thus, a substantial need exists for collection and transport devices that will yield viable organisms after four hours storage time.
The prior art clearly discourages the use of dry swabs. Similarly, it universally utilizes fibrous swabs of cotton, wool, rayon, polyester, and calcium alginate. Among the materials not previously used in swabs for collecting and transporting microorganism is polyurethane. At least one study, Bach, John A., et al., "Inhibition of Microbial Growth by Fatty Amine Catalysts from Polyurethane Foam Test Tube Plugs", Appl. Micro. Biol., vol. 29 no. 5, pp. 615-620 (1975), has concluded that the material is not suitable for use when culturing microorganisms because autoclaving the polyurethane releases substances which are toxic to microorganisms.
Another acknowledgment that polyurethane may harm an organism with prolonged contact is found in U.S. Pat. No. 4,401,130 to Halford et al. That patent addresses the problem of joining a polyurethane foam swab to its stick without leaving dust which it characterizes as "possibly dangerous when open wounds are subject to treatment using the swabs." Col. 2, lines 27-8.
Polyurethane has been used in other health care applications. For example, one brand of contraceptive sponge is made from a special grade of polyurethane foam made from a foamable hydrophilic prepolymer resin available from W. R. Grace Co. and sold with the trademark Hypol. These resins are derived from toluene diisocyanate and methylenediphenyl diisocyanate. They have also been used in wound dressings. The polymers made from these resins are said to have no extractable toluene diamine, toluene diisocyanate, or other primary aromatic amines.
Polyurethane is recommended for use in a unitary molded swab described in U.S. Pat. No. 3,871,375. That patent states that the swab may be used for "application of medication, the removal of earwax, and all of the other uses for which swabs are normally employed." Col. 2, lines 16-18. It also states that the swab may be sterilized. It does not suggest use for collecting biological specimens and therefore does not address the known toxicity of polyurethane to microorganisms.
Additionally, polyurethane foam has been reported to be useful as a swab tip for removing foreign materials from a surface and to apply fluids such as paint, cosmetics, and medicines. U.S. Pat. No. 3,724,018 describes a swab made with a reticulated plastic foam material, such as polyurethane foam, wrapped around an end of a stick. The patent does not address sterilizing the swab or the known toxicity of polyurethane to microorganisms.